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# How many hours, minutes and seconds in a day, and why it happened

How many hours do you have in a day? Everyone knows this - 24 hours. But why did it happen? Let's take a closer look at the history of the emergence of the basic units of time and find out what day is, how many hours, seconds and minutes. And also see if it is worth attaching these units exclusively to astronomical phenomena.

Where did the day come from? This is the time of one revolution of the earth around its axis. Little else is known about astronomy, people began to measure time by such ranges, including in every light and dark time.

But here there is an interesting feature. When does the day begin? From the modern point of view, everything is obvious - the day starts at midnight. People of ancient civilizations believed otherwise. It is enough to glance at the very beginning of the Bible, in order to read in Genesis 1: "... and there was evening, and there was morning day: day one". Day began with the sunset. There is a certain logic in this. The people of those days were guided by a light day. The sun has set, the day is over. Evening and night - this is the next day.

But how many hours in a day? Why was the day divided for 24 hours, because the decimal system is more convenient, and much more? It would be in a day, say, 10 hours, and in every hour 100 minutes, then something would change for us? Actually, nothing but numbers, on the contrary, would even be more convenient to perform calculations. But the decimal system is far from the only one used in the world.

In ancient Babylon, a sexagesimalaccount system. And the bright half of the day was well divided in half, for 6 hours each. Total in 24 hours a day. This is a fairly convenient division took from the Babylonians and other peoples.

The ancient Romans counted the time stillmore interesting. The countdown began at 6 am. So they considered from this moment on - the first hour, the third hour. Thus, it can be easily calculated that the "workers of the eleventh hour" commemorated by Christ are those who begin work at five o'clock in the evening. Indeed, it's too late!

At six o'clock in the evening the twelfth hour came. That's how many hours in the clock counted in ancient Rome. But there were still night watches! The Romans did not forget about them either. After the twelfth hour, night guards began. The duty was changed at night every 3 hours. Evening and night time was divided into 4 guards. The first evening guard began at 6 pm and lasted until 9. The second, midnight, lasted from 9 to 12 hours. The third guard, from 12 am to 3 am, was finished when the roosters sang, that's why it was called "singing roosters". The last, the fourth guard, was called "morning" and ended at 6 am. And it all began again.

The need to divide into component parts alsothe clock arose much later, but from the sexagesimal system did not retreat and then. And then the minute was divided into seconds. True, later it turned out that to rely only on astronomical observations to determine the duration of seconds and days can not be. Over a century, the duration of the day increases by 0.0023 seconds - it seems to be very little, but enough to get confused about the question of how many seconds in a day. And this is not all the complexity! One revolution around the Sun our Earth does not for an equal number of days, and this also affects the decision of the question of how many hours a day.

Therefore, to simplify the situation, they equated the secondnot to the motion of celestial bodies, but to the time of the course of processes inside the cesium-133 atom at rest. And to match the actual state of affairs with the circulation of the Earth around the Sun twice a year - December 31 and June 30 - add 2 extra leap seconds, and once in 4 years - an extra day.

Total it turns out that in the 24 hours, or 1440 minutes, or 86400 seconds.

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